In the petroleum industry at the present time, many different exploration and production operations can be carried out with respect to petroleum producing wells through the use of continuous tubing which is typically referred to as coiled tubing. Coiled tubing for use in wells is typically stored on a large reel and is run into and out of oil and gas wells in much the same way as wireline cable. Coiled tubing has become especially advantageous in the drilling, completion, and production of petroleum producing wells that are drilled in such manner that significant portions of the well bore are substantially deviated from the vertical or translated from the vertical to horizontal or near horizontal so that a well bore of significant length can be located within a very narrow petroleum production zone.
Coiled tubing is also extensively utilized in the positioning and manipulation of hydraulically energized downhole devices that accomplish various operational activities in deep petroleum producing wells. For example, through the use of coiled tubing which can be quickly run into a well, various servicing activities can be conducted such as setting packers and plugs, circulating heavy fluids out and replacing them with lighter fluids or by replacing fluids with a gas such as nitrogen. Coiled tubing also finds efficient use in other well servicing activities such as perforating the well casing, killing the well or producing the well. These operations are typically conducted by applying pump pressure within the internal passage of the coiled tubing to manipulate various downhole devices by means of hydraulic pressure.
More recently it has been determined that various other desirable downhole working operations can be accomplished by installing an electrical logging cable inside the coiled tubing and accomplishing logging functions while carrying out hydraulically energized downhole operations in the manner set forth above. Although the use of coiled tubing with electrical logging cable inside is desirable, installation of logging cable within coiled tubing can be difficult and expensive. It should be born in mind that coiled tubing for a rather deep well can be more than 15,000 feet in length.
In the past, the processes utilized for installation of electrical logging cable within coiled tubing has taken two general forms. One cable installation procedure is accomplished by uncoiling the tubing onto a long deserted or seldom traveled stretch of road and by then pumping the electrical cable into the horizontally oriented coiled tubing by hydraulic pressure using a cup seal attached to the logging cable to provide a locomotive force to the cable. This activity is accomplished by passing the electrical cable through a stuffing box to permit hydraulic pressure build-up within the coiled tubing upstream of the cup seal to develop a pressure differential across the cup seal that develops the motive force for cable insertion. This procedure causes a number of disadvantages. It is difficult to gain access to three to four miles of fairly flat deserted roadway. It is difficult to locate a road that will remain deserted long enough to complete tubing layout, logging cable installation, and recoiling of the tubing. It is also difficult with the coiled tubing lying flat to apply the correct tension to the logging cable as it is installed inside the horizontally located coiled tubing because the cable tends to increase tension or shorten when the tube is spooled up onto a coiled tubing reel. As the logging cable is pumped or forced into the horizontally located coiled tubing by means of hydraulic or pneumatic pressure to the cup seal, the initial portion of the cable is dragged along the inside surface of the coiled tubing. The surface contact that occurs between the logging cable and the coiled tubing tends to erode the electrical insulating material of the coiled tubing especially if the tubing has any internal roughness projections or other irregularities. Obviously, any wear or erosion of the electrical logging cable is undesirable and may be unacceptable.
The other frequently used process for installing electrical logging cable inside coiled tubing is to locate a well deep enough to lower all of the tubing into. This well must of course be abandoned from the standpoint of petroleum production. To accomplish this type of cable installation the coiled tubing is run into the well and appropriately supported at the surface. A cup seal is fixed to the lower end of the electrical logging cable and is pumped down into the vertically suspended coiled tubing in the same manner as discussed above in connection with the horizontal cable installation procedure. In this case, however, the weight of the electrical logging cable is employed to advantage for its installation into the coiled tubing. Also in this case, the electrical logging cable will be worn to some extent by rubbing against the inside surface of the coiled tubing but its wear will typically be substantially less than the wear that occurs during the horizontal logging cable installation procedure. A few abandoned petroleum wells are provided by well owners for installation of logging cable into coiled tubing. These abandoned wells must be maintained and inspected regularly and thus represent a significant expense to the well owners. Obviously, to recover well maintenance expenses and to provide a profit for the well owners, users will incur significantly high costs paid for use of the well for the purpose of logging cable installation. This well use cost of course represents a commercial disadvantage which is overcome by the present invention. Further, for installation of logging cable within coiled tubing, the tubing must be transported to the site of the abandoned well, and after installation of the logging cable, must be again transported to an appropriate site for storage or for use. The expense of such transportation is another commercial disadvantage that is overcome by the present invention.
It is desirable, therefore, to provide a method and apparatus for the manufacture of coiled tubing with electrical logging cable being positioned within the coiled tubing during the manufacturing process. The provision of the coiled tubing in this manner avoids the requirement for sparsely traveled roads or the use of abandoned wells for installation of electrical logging cable inside previously manufactured coiled tubing. It is desirable also to provide a coiled tubing/electrical logging cable assembly wherein the logging cable is protected from erosion or other types of deterioration during the manufacturing process for the assembly.